KX3 Power cable

[Dave Sublette-2]

Good morning,

I am using the standard power cable that is supplied with the KX3.  Using a
digital multi meter and the built in voltage monitoring capability of the
KX3, it looks like the supply voltage is dropped by 0.5 volts in the power
cord when transmitting with 5 watts  According to the built in monitor, the
KX3 is pulling 1.6 amps from my gel cell.

The gel cell voltage drops also, but I compensated for that when I
calculated the .5 volt drop in the power cord.

It seems to me that a larger gauge wire is called for in the power cord.

Also, I can't get the KX3 to transmit more than 5 watts.  If I turn the
power up to 10 watts, it transmits at that level briefly, then turns the
power down to 5 watts.  It must be some voltage sensing circuit that does
it.  The supply voltage is showing 11.4 VDC when keyed..

So what about the gauge of wire for the power cord?  Do you think we need a
larger sized wire?

73,

Dave, K4TO
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[N0WL]

Dave,

I sell a product at http://stores.ebay.com/N0WL-Radio that goes a long
way to solving your concern.  It is a Anderson PowerPole adapter for the
KX3. (I have designs for the KX2 and FT-817 also.)

This adapter uses a 3D printed shell to securely attach the adapter to
the KX3, keeping the length of the low gauge wire to an absolute
minimum.  There are other advantages to using an adapter like this - you
can see them on the website.

Please note that this current design cannot be used with an after-market
heat sink.  I will have another product for that shortly. Elecraft uses
available space on the left side of the radio so efficiently that it is
very hard creating a design that I would be happy to take into the field.

jon poland, n0wl


On 1/31/2018 08:49, Dave Sublette wrote:

> Good morning,
>
> I am using the standard power cable that is supplied with the KX3.  Using a
> digital multi meter and the built in voltage monitoring capability of the
> KX3, it looks like the supply voltage is dropped by 0.5 volts in the power
> cord when transmitting with 5 watts  According to the built in monitor, the
> KX3 is pulling 1.6 amps from my gel cell.
>
> The gel cell voltage drops also, but I compensated for that when I
> calculated the .5 volt drop in the power cord.
>
> It seems to me that a larger gauge wire is called for in the power cord.
>
> Also, I can't get the KX3 to transmit more than 5 watts.  If I turn the
> power up to 10 watts, it transmits at that level briefly, then turns the
> power down to 5 watts.  It must be some voltage sensing circuit that does
> it.  The supply voltage is showing 11.4 VDC when keyed..
>
> So what about the gauge of wire for the power cord?  Do you think we need a
> larger sized wire?
>
> 73,
>
> Dave, K4TO
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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[hhoyt]

Dave,

The vast majority of the voltage drop you see is not in the DC Power cable, it is in the anti-parallel polarity protection diode in the KX3 itself and all KX3 users see this drop regardless of what gauge cable you power the KX3 with.  A 1 M length of 18 gauge cable will drop less than 0.1 V at the maximum current of 2.5 A the KX3 can draw at 15 W.

Your internal voltage reading of 11.4 V is too low for the KX3 to allow operation over 5 W, and the problem is your power supply voltage is too low.  I suggest you use a power supply which delivers at least 13.8 V with a receive load of 0.2 A.  That will fix your transmit power issue, and it is the reason we designed the Kx33 Low-RFI power supply to output 14.2 V at a KX3 receive load of 0.2 A.  There are other advantages as well to this higher supply voltage such as higher power output with lower IMD in digital and SSB modes.

Cheers & 73,
Howie - WA4PSC
www.proaudioeng.com


>>I am using the standard power cable that is supplied with the KX3.  Using a
>>digital multi meter and the built in voltage monitoring capability of the
>>KX3, it looks like the supply voltage is dropped by 0.5 volts in the power
>>cord when transmitting with 5 watts

______________________________________________________________
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